This invention relates to pressure release devices for internally pressurized fluid containers.
Pressurized fluid containers are in widespread use for packaging and dispensing a variety of fluid products, including liquids, gases, solids and combinations thereof. Under normal operating conditions, such containers perform entirely satisfactorily. However, in the event that the contents of such containers become over-pressurized, either because of improper use, exposure to heat or for any other reason, then a violent rupture may occur. For the last 28 years, those skilled in the art have been attempting to solve this problem by incorporating various types of pressure release devices into the container structures. Examples of some of these previously developed pressure release devices are disclosed in U.S. Pat. Nos. 2,795,350 (Lapin); 3,292,826 (Abplanalp); 3,512,685 (Ewald); 3,622,051 (Benson); 3,724,727 (Zundel); 3,786,967 (Giocomo); 3,815,534 (Kneusel); 3,826,412 (Kneusel); 3,831,822 (Zundel); 4,003,505 (Hardt); 4,347,942 (Jernberg et al.); 4,416,388 (Mulawski); and 4,433,791 (Mulawski). In these prior art devices, scored or coined lines of reduced material thickness are caused to fracture in response to an overpressurization of the container contents, thereby creating vent openings.
Other types of pressure relief devices are disclosed in U.S. Pat. Nos. 2,951,614 (Greene); 3,356,257 (Eimer); 3,515,308 (Hayes); 3,759,414 (Beard) and 4,158,422 (Witten et al.).
Of the foregoing devices, it appears that only those disclosed in the Giocomo U.S. Pat. No. 3,786,967 and Mulawski U.S. Pat. No. 4,433,791, patents have achieved any significant measure of commercial acceptance. Such devices, however, are difficult and expensive to manufacture in the large quantities needed to fill existing commercial demands. The problem stems from the need to consistently maintain a prescribed coin depth along the line or lines surrounding either a pressure release tab or a rim of the container. This is particularly true of the device disclosed in the Mulawski U.S. Pat. No. 4,433,791, patent where for example, when manufacturing the device from sheet steel having a thickness of 0.015", the coined depth must be maintained within an extremely narrow range of between about 0.0015" and 0.0025" in order to insure that pressure is released within a range of between about 210 to 250 psig. A shallower coin depth will result in an unacceptably high pressure release, thereby presenting a risk that the container bottom will be blown off. On the other hand, a deeper coin depth may produce a prematurely low pressure release, in addition to encouraging the development of micro cracks in the remaining relatively thin membrane at the base of the coined line. These micro cracks may not always be detectable at the time of manufacture. They may occur later after the container has been filled with a pressurized product, thereby resulting in leakage and potentially costly losses.
Thus, the manufacturing process must be carefully monitored with particular attention to timely equipment adjustments to compensate for tool wear, and, when appropriate, to replace worn tools. This requires frequent product sampling and testing, all of which significantly increases manufacturing costs.
The objective of the present invention is to provide an improved and highly effective pressure release device which is entirely free of scored or coined lines, thereby obviating many of the above-described production problems associated with the prior art devices.